Engine fuel consumption during specific load ranges can be reduced by shutting down a number of engine cylinders, called part-load operation.
The efficiency of a petrol engine during part-load operation can be perceptibly increased by partial engine shutdown. At a constant engine power, switching off one cylinder of a multi-cylinder engine increases the load on the other cylinders still in operation. Thus a throttle valve arranged in the intake system may be opened further to introduce a larger air mass into these cylinders to achieve de-choking of the internal combustion engine. The cylinders that remain in operation during the partial shutdown may thus operate in a higher load range, reducing fuel consumption. Thus, the collective load may be shifted towards higher loads.
Because of the greater air mass supplied during partial shutdown, the cylinders which are still in operation may also have a more homogenous mixture formation and tolerate higher exhaust gas recirculation rates.
Further efficiency advantages arise from the absence of combustion because a cylinder which is switched off may not generate wall heat losses resulting from a heat transmission from the combustion gasses to the combustion chamber walls.
Due to high emission quality regulations, diesel engines (auto-ignition engines) may have a higher efficiency or lower fuel consumption than petrol engines in which the load may be set via quantity regulation by the filling of the cylinders with fresh mixture. However, in diesel engines the fuel consumption may still be reduced partial shutdown in specific load ranges. Thus, the statements made above in connection with petrol engines apply accordingly to diesel engines.
The multi-cylinder engines with partial shutdown described in the prior art and the associated methods for operating these engines however have significant efficiency losses. In previously disclosed embodiments using partial shutdown during low load operation, cylinders may be grouped into two operating groups such that, during partial shutdown, one of the groups is shut down and the other remains operational. Prior embodiments have cylinder groups in which the two outermost cylinders form one group and the two innermost cylinders another group. In systems utilizing grouped merging of the exhaust gas lines, the exhaust manifolds formed are arranged adjacent to each other along the longitudinal axis of the cylinder head.
However, the inventors found a number of advantages in grouping the cylinder into groups based on cylinder proximity. In a disclosed embodiment, the four cylinders may be configured such that an outermost cylinder and the adjacent innermost cylinder form a group. Further, the cylinders of a second cylinder group may be cylinders which can be switched on in response to engine load, the cylinders of the first cylinder group may be permanently operated cylinders when the engine is in operation.
By grouping cylinders in this manner, an exhaust system and crankshaft could be optimized to separate mutual influence of exhaust during charge change by separating the exhaust of conflicting cylinders having small crank angle (CA) separation. Further, heat may be efficiently preserved in engines during partial shutdown to allow for faster warm up during all-cylinder engine operation and spray oil cooling may be readily suspended to non-operating cylinders.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.